Effect of anaerobic and anoxic selectors on oxygen transfer in wastewater

Pilot- and full-scale systems were operated with and without anaerobic and anoxic selectors to determine the effect of selectors on fine pore diffuser oxygen-transfer efficiency as reflected by the alpha correction factor. All systems operated at a mean cell residence time between 7.0 and 10.0 days and were fully nitrifying. Process water oxygen-transfer performance was monitored using offgas tests. Average measured alpha (alpha) factors in the pilot plant ranged from 0.33 to 0.53 without selectors in operation and from 0.39 to 0.51 with selectors in operation. Average measured alpha factors in the full-scale plant ranged from 0.29 to 0.79 without selectors in operation and from 0.28 to 0.68 with selectors in operation. Both pilot- and full-scale tests indicated that selectors had little influence on oxygen-transfer efficiency as reflected by a when compared with systems that were fully nitrifying.